The present invention relates to the field of correcting images distorted by relative motion between the images and the optical system.
The photographing of the surface of the earth along the line of flight of an aircraft through the use of a scanning slit is well known in the art. Such systems often employ a linear array of photodetectors in conjunction with the slit for converting the picture elements focused upon the photodetectors into electrical signals proportional to the light intensity of the picture elements making up the scene being photographed. The digital arrays may be sequentially scanned and read out, and the analog signals may be converted into digital binary data indicative of the intensity of each pixel, such data being inserted into a digital storage unit. See for example, U.S. Pat. No. 4,257,071. The result is that a first image slice, which takes the form of a digital pulse train representitive of each column of picture elements or pixels extending across the image, is stored within a first column of digital storage elements, and subsequent scan lines of picture elements are inserted into other columns of storage elements. Thus a digital store may contain light intensity information comprising a large number of picture elements, which may subsequently be read out of storage to reconstruct the optical image being scanned by the slit detector unit. Such signals may be telemetered to a distant point e.g., the surface of the earth, and may be employed to modulate a CRT beam or a laser beam for reproducing the optical scene, as is well known by those skilled in the art. Exemplary photodetector arrays and processing of the data read out of the arrays may be found in U.S. Pat. Nos. 4,064,533; 3,808,435; 3,883,437.
If the linear detector array is positioned perpendicularly with respect to the line of flight, shifts in the relative position of the slit detector unit with respect to the viewed surface of the earth will cause shifts in the relative positions of the picture element pulse trains inserted into the columns of storage elements, and if the storage elements are later sequentially readout, a distorted image is thus produced. These shifts are often produced due to camera vibration and aircraft roll.
It is thus a primary object of the present invention to eliminate these shifts between the stored lines of pixel pulse trains by electronically transforming the relative position of the pulse trains with respect to each other, thereby to eliminate the readout of a distorted image.
It is a further object of the invention to detect the degree of shift from one line of stored digital pixel data to the next, and produce a shift signal which is employed to transform the relative positions of the data to an extent and in directions to eliminate image distortion upon readout.